1st Gen R53 Cooper S Random Misfire - P0300

Yesterday I loaded up the Mini to head to Road America, but I didn't get far. 15 miles in, cruising at 65mph, the engine sounded rough, loss of power (limp mode?) and when off the freeway, the car was barely able to move from a stop. We stopped at a gas station, turned it off, started, all good again. Scanner told me the car had a random misfire, but no reasons.

The realtime mpg read 99.9mpg from the moment the problem began until the engine was restarted. Not sure if that means anything.

Drove it home on side roads and all was good. The car ran fine for the last 50 miles prior to this trip. All that was different was the addition of 7 gallons of cheap Costco gas the night before. Water in gas?

I googled for the code but not much can be found that helps. I have no time to look into it until later in the week, but any suggestions where to begin checking are welcome.

 

plugs wires and coil have less than 2500 miles on them. Installed last year. No problem before the misfire. That is one thing I actually didn't replace this time around.

all cylinders misfiring points at coil, but I don't understand why it would do it at cruising speed and then, after the engine is turned off and turned back on be fine for the next 20 minutes of driving (at lower speed, though, but with some pulls through the gears).

When I have time I will pull the plugs and take a look. I still have a fully functional coil, two sets of wires, and two sets of plugs throw at it, but I just can't imagine this problem would come about like this.

I read about intercooler boot leaks causing misfires, but if it leaks, why would it take this long to cause a problem, and then be fine again after a computer reset. The code actually went away without me clearing it, only found it stored in my Android App I run to monitor coolant temp and other things. Coolant was at a perfect 188-195 (I replaced the thermostat and gasket recently, full flush and new coolant in there). I did smell coolant though, when I parked it, but I figured it was from the recent change when it went all over the car. No coolant leaking on the ground.

No time to look at the car until Monday or Tuesday though. Thanks for the suggestions.

 

wires are Bosch but meant for the car, coil is for a Subaru but fits. Only thing I could find in the desert last year when I had different problems with the car. Worked fine over the Rocky Mountains last year.

The reason I mentioned fuel - it's the only thing that changed from the day before. I read about people getting water out of gas pumps when those hit the bottom of the tank. Car sat overnight and it may have pooled at the bottom of my tank then. Jus ta guess.

Car also idled funny every time I turned on the AC since I had it all apart. Works, though. That morning was the first time I ran the AC for a good distance. Turned it off when the problem started. Can't really figure out why that would cause a misfire, though.

 

there's nothing wrong with the coil. Car ran 20 miles immediately after restarting it without a hiccup.

I have an OEM coil in the bin, corroded terminals and all, the full package you get from Mini for your money. I can throw it on, but I don't see the point right now after having driven that car for 3000 miles and over mountain passes with that coil. Plus I don't believe that a coil sold as a OEM replacement for this car would fry the ECU. Maybe the MSD thing, but this is what a European shop that fixes BMWs ordered for me when we were about 350 miles away from any Mini dealer and had some strange cutting out issues on long uphill runs (full engine shutdown then - unrelated to this issue, but the reason I replaced full filter and pump after all the coil/wire/plug changes were a total waste of money, as the problem continued while in the mountains - and no engine codes then, no misfire, just off, second later bump started itself and went on)

The gas isn't old - new fuel pump and filter went in in April when the tank was near dry. Gas was fine before and after the misfire. half the tank was put into the car 12 hours before the drive. The other half may have a few weeks on it. Bad gas is bad gas - car would have misfire all the time. Water on the other hand will accumulate on the bottom of the tank where the pump sucks it in. Doubt that's what it is, though - almost 15 minutes into the drive the car sucks in a water bubble? And then it's immediately gone after engines stop and start? It would still be in the fuel line.

It "idled funny" after I turned on the AC. There's no funny idle if I turn the thing off, plus, that's only when the car is cold. However, it did never do that before. I blame it on the silly powerflex engine mount bushings I am about to pull out anyway. Car never had vibrations and drones before that went on the car.

Boost leak - perhaps, as 3200-3400 rpm on the freeway is a long continued boost situation. However, we did that for 14 miles before the misfire kicked in. Wouldn't such a problem materialize sooner, or when driving at higher boost under harder acceleration? But I will check all the intercooler boots.

The misfire happened at 65mph in top gear while running on flat ground, cruise control on. Sounded at first like the poly engine bushing causing some standing wave drones we had not noticed before, but it got a little worse when trying to accelerate, so we pulled off the road - that's when it barely idled, had to really give it throttle to move past a stop sign to a parking lot. Turned it off, turned it on, all good. No more code light on the speedo once restarted. The mpg real-time readout also worked again after the engine restarted. Before it was pegged at 99.9 mpg

I have not driven it since that day as we were doing 200 miles a day for 3 days back and forth from Road America and had no intention to have the Mini end up on a flatbed for an extended road trip.

I will try to take it for a quick spin around town later tonight, check plugs, see if the intercooler boots are in good shape. They look fine, but maybe something folded under on the bottom where you can't see it. I was quite careful when we put that back together, but you can't really see the bottom of the seal.

 

I understand that it's always safest to go with stock parts. Mini parts were not available in that town in the desert unless I had waited another 2 or so days in motel for several days and had it shipped UPS. I guess I can throw more cash at the car and get a brand new Mini coil. It's just money...

The BMW shop owner said the coil I ordered is identical to a Subaru part when he pulled it up on a computer. It also looks identical to the Mini part - same shape, color, markings, connectors, except for those mounting bolts, which was solved with a trip to the hardware store. I think it's a Bosch part, just like the wires I have on there, all the correct length and made for this engine. it wasn't cheap either. Like I said - it's been in the car for a year. I didn't swap it today, but after cleaning up the terminal on the Mini coil with a wire brush on a drill, I guess I could put it back, except I want to first replicate the problem or find a way that lets me do it on call, so part swap can be verified. With the car running fine, I won't have a clue if it's working

Just ran the car for a 30 mile loop. Easy, then some longer pulls with medium revs, and some pulls from 2000rpm in tall gears. No problem whatsoever doing that. Some time later this week, I'll take it on the freeway. I did not turn on the A/C - slowly working my way up the re-enactment chain to make sure I am not going to find myself stranded.

Pulled the plugs before I went out - all fine. Intercooler boots are seated fine. Boost readings on the Torque App via ODB-II were normal, usually negative down to -10 when rolling downhill in tall gears, and up to +6 at about 4500 rpm. Didn't push it higher yet, and no wide open throttle. No hesitation, no hiccups, all as it was before the misfire. I certainly was at higher boost then the car would have been running at when cruising on the freeway. Water temp is doing the usual yo-yo at 186F to 194F

what about the crank position sensor? How do they fail? Do they let go instantly or do they cause issues and then work again? Probably would throw a different code anyway.

Once I feel more comfortable that the car will make it home, I'll head out on the freeway to do everything exactly the same like when it had the problem. Right now it seems to run just fine.

 

what makes it look bad? I noticed nothing unusual in there when I had the IC off, but then I also didn't go in there inspecting the hose.

Would it leak (as in smell gas?)

 

ok - before I rip off the IC again - which line in this image are we talking about? The black line in front of the fuel rail?

http://www.pelicanparts.com/techarticles/MINI/17-FUEL-Fuel_Pump_and_Filter_Replacement/images_large/pic05.jpg